It will soon call for tenders for companies to design, construct and operate the tunnel. The costs will be recouped through tolls and a $500m Federal Government contribution.

"The project term is about 43, 45 years away," he told reporters, adding that the time frames may change.

Cr Newman likened the council's new approach to the way the Gateway Bridge was constructed, describing it as a necessary project to alleviate congestion for long-suffering motorists.

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Forecasts released by the council suggest the project will cut travel times between the Centenary Bridge and the Inner City Bypass by up to 70 per cent.

The tunnel, due for completion by 2014, is forecast to carry 34,200 vehicles a day when it first opens.

The Lord Mayor, who had struggled to find adequate private sector support for funding the tunnel unless the council guaranteed traffic flows, said he was not prepared to wait five years to resolve the issues.

The sooner the council "put people out of their misery" the better, he said.

However, Opposition Leader Shayne Sutton accused the Lord Mayor of poorly managing the project from the beginning.

"Earlier this year Cr Newman embarked on a $70,000 trip around the world to drum up business for Northern Link, but failed to yield any results," Cr Sutton said in a statement.

Large infrastructure projects were important but the council should ensure ratepayers were not "unfairly burdened" by large debt and rates rises, she said.

Cr Newman brushed off suggestions the council's decision to go it alone would increase rates in coming years.

He said the council would ensure it was disciplined with its spending decisions and would keep "tight control" over the project to avoid cost blowouts.

"My biggest concern ... is to make sure we get the best possible competition during the tender process," he said.

Cr Newman would not reveal the anticipated toll amount, saying it would be revealed when the council announced the winning tender for the tunnel's construction and operation.

The council is set to borrow the money for the tunnel from the Queensland Treasury Corporation, with construction tipped to begin by Christmas next year.

Councillors will debate the new expressions of interest process at a meeting on Tuesday.